Question

I recently integrated base64-encoded embedded images as attachments for an e-mail system I’m programming for a start-up. Are base64-encoded embedded images really worth it? I was only able to find one article regarding email clients and blocking base64 embedded images but it doesn’t make sense that companies such as LinkedIn continue to embed images regardless if this was the case.

Answer 1

This is mostly speculative but the only reason I can imagine you getting spam-trapped for having an inline image in your email is because spammers commonly insert an inline image as their primary message content, and only a small amount of filler text in the message to make it look like something else was the main subject matter.

They may have mistaken your email as such spam. I would question whether the inline image was the only factor for this though.

The obvious advantage to this method is if you have one or two images you want displayed in your emails automatically, you can accomplish it with an inline image. If you refer to an image from an external URL, then most email clients will require the user display images, or add you to their allow list. For display purposes, I would limit this to one or two images. Some email clients may show them as attachments or refuse to show them inline, and if you had 20 inline images, that may look strange.

I’d look into what spam filter blocked your message or if it was a corporate email account like Microsoft/Gmail, then you may just have to do some experiments and research.

Aside from that, check into additional verification measures you can use on your mail server to help other servers trust it more such as SPF, DKIM, and making sure your PTR records are all sorted.